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Jacki

Senior Member

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Posts: 237

Ringing problem of TIA amplifier.
May 02^nd, 2013, 3:59am

Hi,

I face a ringing problem for trans-impedance amplifier. Actually it is not oscillation, it looks like overshooting. But the Opamp in TIA has enough phase margin (80 degree). I cannot figure it out. In the book, usually the phase margin is defined for voltage source, I don't know if it could be used for current source.

But if I change current source to voltage source as shown in the figure, I don't have any problem of ringing (overshooting). Because the phase margin of loop gain is around 80 degree, I can see the overdamping for voltage source.

Could anyone give me some comments?

Thank you.

Jacki.

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raja.cedt

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Germany

Re: Ringing problem of TIA amplifier.
Reply #1 - May 2^nd, 2013, 7:04am

hello,

While calculating Loop gain or Phase margin why input come into picture? you should make current/voltage=0
You could have use voltage source in series with resister rather //, then both cases will give same PM.

BTW did you check differential PM or single ended PM, check only differential PM Try to use cmdprobe. Show me how amplifier looks Inside.

Thanks,
Raj.

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Jacki Senior Member Offline Posts: 237	Re: Ringing problem of TIA amplifier. Reply #2 - May 2^nd, 2013, 7:23am Hello Raj. Thank you very much for your comments. I find the possible problem, it could be a zero due to the feedback resistor (there is a feedthrough path). So I need a feedback capacitor Cf in parallel with Rf to generate a pole to compensate this zero. Then ringing problem is solved. Jacki.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: Ringing problem of TIA amplifier. Reply #3 - May 2^nd, 2013, 9:21am Hello, If there is no ringing problem then fine, but please note that frequency independent feed-forward path can't generate a zero in the open loop. Generally people use parallel capacitor to create zero which can compensate extra pole's in the loop. Thanks, Raj.
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Jacki Senior Member Offline Posts: 237	Re: Ringing problem of TIA amplifier. Reply #4 - May 3^rd, 2013, 5:37am Hello Raj. Thank you very much for the correction, I think it is the low pass filter for the feedback loop. Jacki.
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Kevin Aylward

Community Member

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Posts: 52

Re: Ringing problem of TIA amplifier.
Reply #5 - Jul 6^th, 2013, 6:11am

The voltage driven circuit, as drawn is being driven incorrectly. As drawn, there is NO feedback at all because it is all shorted out by the voltage source. That�s why it would show no ringing if simulated as drawn. It is attempting to run the TIA as an open loop amplifier! The resisters need to be put in series with the voltage source in order to have any meaningful result when voltage driven.

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Kevin Aylward

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